1. Field of the Invention
The present invention generally relates to the field of inspection and analysis of specimens and, more particularly, to void characterization in integrated circuits.
2. Description of Related Art
The metallization and thin film layers of conventional integrated circuits contain interconnects such as vias, contacts, and windows. The interconnects are arranged to allow electrical contact between transistors and other circuitry in the integrated circuit. However, a variety of factors may cause the formation of voids in the conductive layers. Voids can interfere with electrical contact between various circuit elements. Voids may be caused by factors such as stress, electromigration, and impurities. As line widths continue to decrease in size, even relatively small voids are extremely harmful. Voids can lead to open circuits and ultimately failure of the integrated circuit.
Inspection of integrated circuit at various stages of manufacture can significantly improve production yield and product reliability. If a void can be detected early in production, the cause of the void can be determined and corrected before a significant number of defective IC""s are manufactured.
Conventional defect detection systems frequently use the xe2x80x9cvoltage contrastxe2x80x9d technique. The voltage contrast technique operates on the basis that potential differences in the various locations of a sample under examination cause differences in secondary electron emission intensities when the sample is the target of an electron beam. Thus, the potential state of the scanned area is acquired as a voltage contrast image such that a low potential portion of, for example, a wiring pattern might be displayed as bright (intensity of the secondary electron emission is high) and a high potential portion might be displayed as dark (lower intensity secondary electron emission). Alternatively, the system may be configured such that a low potential portion might be displayed as dark and a high potential portion might be displayed as bright.
A secondary electron detector is used to measure the intensity of the secondary electron emission that originates only at the path swept by the scanning electron beam. A defective portion can be identified from the potential state of the portion under inspection. In one form of inspection, the mismatched portion between the defective voltage contrast image and the defect free one reveals the general defect location.
Other techniques for defect detection involve slicing a wafer into cross sections and using an electron microscope to locate defects. Intrusive methods, however, are both time consuming and wasteful. Acoustic and optical methods are also available, but can only be used in very particular circumstances. The acoustic techniques require significantly more time to collect adequate data for a statistically significant sample. Additionally the acoustic techniques can not address transparent films and are limited in the lower (few nanometer) film thickness range.
Using the voltage contrast technique allows a general determination of the location of defects in the sample. However, conventional voltage contrast techniques do not allow thorough characterization of a void. For example, voltage contrast does not provide sufficient information about the type of defect, size, or exact location including the depth of the void. Accordingly, improved detection systems allowing more precise characterization of voids are desirable.
The present invention provides a system for characterizing voids in test samples. An x-ray emission inducer scans a target such as a via on the test sample. A metallization or thin film layer emits x-rays as a result of the scan. The x-ray emission intensity can be measured and compared against a control measurement. The information obtained can be used to characterize a void in the scan target.
In one embodiment, an apparatus for characterizing a void in a first scan target associated with a sample having a first surface and a second surface is provided. An x-ray emission inducer is configured to scan a first scan target. The x-ray emission inducer causes the first scan target to emit x-rays from the first surface. An x-ray emission detection system is configured to obtain a measurement of the x-rays emitted from the first surface of the sample. The x-ray measurement is compared to a control measurement to characterize a void in the first scan target.
In another embodiment, a system for characterizing voids associated with a sample having a first surface and a second surface is provided. The system includes a memory and a processor coupled with memory. The processor is configured to identify a first measurement of induced x-ray emissions characteristic of a first material at a first scan target, identify a control measurement, and provide the first measurement and the control measurement for comparison to thereby obtain information for characterizing a void associated with the first scan target in the sample.
In still another embodiment, a method for characterizing a void in a sample is provided. A first measurement of induced x-ray emissions characteristic of a first material at a first scan target is identified. A control measurement is identified. The first measurement and the control measurement are provided for comparison to thereby obtain information for characterizing a void associated with the first scan target in the sample.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example various principles of the invention.